This project proposal will focus on four main areas: 1) Functional and structural studies on the activation of the first component of complement (C1) and its subunits by antigen antibody complexes and enzymes derived from the kinin forming system; 2) Structural studies on the fourth (C4) and the second (C2) components; 3) Interaction of complement with amyloid proteins and activation by IgA immunoglobulins; 4) The nature of a complement independent phagocytosis enhancing factor (PEF) and its relationship to the immunoglobulin binding factor (IBF) produced by stimulated lymphocytes.